1. Field of the Invention:
The field of the invention is related to oscillators or clock circuits specifically the field of the invention is low phase jitter clock circuits.
2. Art Background:
Clock generators are typically used to synthesize delay times in delay generators, and to produce other related frequencies in frequency synthesizers. A clock generator produces a stream of pulses which are equally spaced in time. Generally, crystal oscillators are used for these clock generators due to their accuracy and simplicity. However, crystal oscillators are very hard to synchronize with an external triggering event. When a delay needs to be synchronized when an external trigger pulse, the need for coherence between the clocks is important.
If there is no coherence between the trigger initiating a delay and the clock whose cycles are counted to synthezise a delay, the resulting delay will be in error by as much as one clock cycle time. If the trigger pulse, by some fortunate accident, happens to be exactly coincident with one pulse in the clock generator, there will be no error in generating the proper delay time. However, this is seldom the case and generally the trigger, which is an independent event, will fall somewhere between two pulses of the clock generator. The time from the trigger pulse to the next clock pulse is unwanted and is called jitter. Jitter is thus a random variation in the desired delay time.
It is desirable to have an accurate clock which is coherent with the trigger pulse. It is also desirable to be able to adjust the frequency of the clock by a simple and stable means.